Electrochemical Noise Measurement of Pitting Corrosion of Stainless Steels in Potash Brine Solution at Elevated Temperatures

This thesis explored the use of electrochemical noise measurement (ENM) as a tool to evaluate for the presence of pitting corrosion in saturated potash brine solutions at elevated temperatures. The materials investigated in this study were AISI 316L (UNS S31603) austenitic stainless steel used as a reference, Rolled Alloys AISI 2205 (UNS S32205), Zeron 100 (UNS S32760), and Ferralium 255 (UNS S32550) duplex stainless steels. These materials were tested to identify if the data acquired from ENM could be used to identify pitting corrosion under these conditions. A secondary focus was to determine a method of data analysis to identify how this tool could be used to rank the propensity for pitting corrosion of each alloy. The study involved preparing cylindrical samples of the selected materials and exposing them to a controlled saturated potash brine environment at 25 ºC, 50 ºC, 65 ºC, and 80 ºC. The electrochemical noise data generated by pitting corrosion was measured using a zero resistance ammeter, with the test cells placed in a thermally insulated Faraday cage. The data was analyzed statistically and spectrally to identify if pitting corrosion could be identified using this technique. The occurrence of pitting corrosion was confirmed with optical microscopy and scanning electron microscopy. The data allowed for a relative pitting resistance order to be concluded below critical pitting temperatures. Key findings demonstrated that ENM is an effective method for identifying pitting corrosion in addition to determining a relative corrosion resistance of materials using statistical analysis, time domain analysis, and power spectral density plots. Among the materials tested, Zeron 100 and Ferralium 255 exhibited fewer and less severe corrosion events compared to AISI 316L and Rolled Alloys 2205, indicating superior resistance to pitting corrosion. The results of this research provided valuable insights into the selection of materials for use in potash processing environments, where high chloride concentrations and elevated temperatures are prevalent. This study offers a methodology for ranking the corrosion resistance of different stainless steel grades using ENM and contributes to the understanding of pitting corrosion in potash processing.